From Microsystems Technology: Fabrication, Test & Reliability

1 Overview

The production of microstructures by the LIGA process is schematically represented in Fig. 1 and 2. The essential process steps are X-ray lithography with synchrotron radiation, the electroplating of metals and the molding of plastics. This combination of process steps have been given the name LIGA; LI for X-ray lithography, G for galvanic or electroplating and A for Abformung (German word for molding). In X-ray lithography, as a first step, a plastic layer several hundreds of micrometers thick is applied to a metallic base plate or an isolated plate with an electrically conductive cover layer used as the substrate. The X-ray sensitive plastic is either polymerized in place directly on the base plate or glued to it. Until now PMMA (polymethyl methacrylate) has been used almost exclusively as X-ray resist because of its high contrast known from electron beam lithography. To form the micro structure an absorber pattern of a mask is transferred into the thick plastic layer with the aid of extremely parallel and high intensive synchrotron radiation with a characteristic wavelength between 0.2 and 0.6 nm. The X-ray radiation which passes through the mask is absorbed in the resist and leads to a chemical modification. In the case of PMMA the chemical resistance changes because of bond breaking in the long molecular chain, so that these regions can be dissolved with a...

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Lithography equipment transfers circuit or device patterns onto a substrate using a patterned mask and a beam of light or electrons to selectively expose a photoresist layer. Overlay metrology systems align the pattern masks or reticules.

3.1 Basic Microtechniques
This section aims to provide the readers an overview of basic microtechniques, which are not only used for microfluidics but also for microelectronics and MEMS. Refer to [1]...